Hybrid open-end multilevel six-phase machine drive system with reduced harmonic distortion

In this paper, a new hybrid multilevel six-phase machine drive system topology is proposed and investigated. Such topology is composed of two three-level three-phase neutral-point-clamped (NPC) inverters and a traditional two-level three-phase voltage source inverter (VSI) with isolated DC-links feeding the open-end windings (OEW) of a six-phase induction motor (SPIM). The system model, operating principles, investigation of the common-mode voltage (CMV) generated and two space vector pulse width modulation (SV-PWM) strategies are presented. The first SV-PWM technique is based on three similar individual plans and its implementation by means of equivalent level-shifted PWM (LS-PWM). The second technique is based on multidimensional approach. Both techniques used are able to generate multilevel voltage waveforms with reduced switching stress, which is suitable for high power applications with voltage and current restrictions. The performance of the system is compared with a standard configuration. It has demonstrated some advantages such as: (i) reduced number of isolated DC-link capacitor banks, (ii) lower harmonic distortion of the machine currents, (iii) possibility to use three different ratios of DC-link voltage. The feasibilty of the system is demonstrated by simulation and experimental results.